Two more people have been arrested over the felling of the Sycamore Gap tree in September.
Northumbria Police said two men in their 30s were arrested in connection with the incident and both have been released on bail.
Soon after the tree was felled a 16-year-old male and a 60-year-old man were arrested and later bailed.
The tree in Northumberland, believed to have been about 300 years old, was cut down overnight between 27 and 28 September in what police believe was a deliberate act of vandalism.
Detective Chief Inspector Rebecca Fenney-Menzies, of Northumbria Police, said: “The loss of Sycamore Gap has been felt deeply across the community as well as further afield.
“As a force, we have seen many touching tributes from those who have detailed what this iconic landmark meant for them personally and for our region.
“We’ve been working tirelessly to identify anyone responsible and bring them into police custody and we are committed to getting justice.”
Historic England previously said Hadrian’s Wall was damaged when the tree was felled.
Work to remove the tree from the delicate Roman wall was described as a “complex and difficult” operation by the National Trust.
The world-famous tree, which featured in the 1991 Hollywood blockbuster Robin Hood: Prince Of Thieves, was too big to move in one piece.
Chainsaws were used to remove branches before a crane lifted the 50ft tree off the wall.
It was then taken away from the area and put into safe storage at a trust site.
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The much-photographed and painted lone sycamore was based in a dip in the Northumberland landscape.
There will be public consultation about what happens next at the site, which has UNESCO designation and is a Scheduled Ancient Monument.
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